Tuesday, 5 March 2019

Purple Sweet Potato Mousse Cake

Just a few days to my official handover..

Feeling a little sad because after all I have met a lot of nice people around here. 
But life still goes on, right?

Had a birthday celebration with out Corgi friend yesterday at Kilo Kitchen. Very nice place and vibes, food is of Taco Fusion and a little bit of Asian infused. A pretty nice place to chill and food is very good. Staff are very attentive and nice, they even sang a birthday song for my friend.

Baked a Sweet Potato Mousse Cake for this friend as she is a sweet potato lover. She was saying she can whack sweet potato ball everyday in Taiwan.. That's how she loves sweet potato.

First time trying this recipe and I must say the feedback I got was very good. I did some tweak and changes to this recipe but it's still good. Definitely a keep for any sweet potato lovers. 

I used purple sweet potato in this but you may try other types of sweet potato.. 

I do not like this sweet potato custard topping because it is not smooth, I should have blend the sweet potato first before making the custard. If you like to have bits of sweet potato in your cake, you can leave this step out.

In this recipe, I have 3 steps.

Basic sponge, sweet potato mousse and sweet potato custard as topping. 

You may choose to change the sweet potato custard topping to something simple like whipped cream topping. 
Because I already did my sweet potato custard one day before so i decided to use the custard as topping. It's up to own individual preference.

Flying to Hong Kong next week and can't wait to whack all the curry fishball and their milk tea!

Purple Sweet Potato Mousse Cake

Basic Sponge 

4 egg yolks (large)
20g caster sugar
50g corn oil
60g milk
1/2tsp vanilla extract 
75g cake flour
1/2 tsp baking powder
Pinch of salt

4 egg white (large)
1/4tsp lemon juices or 1/4tsp cream of tartar
60g caster sugar

Preheat oven to 180c and lay a 12 x 11 inch swiss roll baking pan with parchment paper.
Separate egg yolk with egg white. 
Whisk egg white until frothy and add cream of tatar, then slowly add sugar in 3 batches and whisk till almost stiff peak foam.
Usual method is to whisk egg yolk mixture first but the reason I whisk the egg white was because I wanted to save time and to wash lesser utensils because you cannot whisk egg whites with dirty whisk.
Put the ready whisk whites at the side first, now we handle the yolk mixture.

Whisk the egg yolk with sugar until light and fluffy. 
Mix corn oil, milk and vanilla extract together, slowly pour into the yolk mixture.
Combine flour, baking powder and salt, sift into yolk mixture. Mix till combine. 
Slightly re-whisk the egg white mixture. Take 1/3 of egg white to fold into egg yolk mixture, first round of mixture is to let it blend in with egg yolk mixture, so the mixture will be slightly deflate. 

Take another 1/3 of mixture and fold in big circles while turning your bowl, mix till no whites and pour in remaining whites to fold again. 
I am using a whisk all the while to mix. you can use spatula as well.
Mix till no white streaks and you are done. Do not overmix otherwise your sponge will deflate and your cake will not be spongy.

Pour cake batter onto prepared pan, lightly tap on counter top to remove air bubbles.
Bake the cake for 10 to 12 mins. Remove from oven and wait for a few minutes before turning cake over. Remove the pan and parchment, let it cool down. 

Sweet Potato Mousse

1 medium sweet potato, steamed and cut into small cubes
100g grams cooked mashed sweet potato
30g sugar
100g milk
60g coconut milk

5g gelatin plus 2 tablespoon water

100g heavy cream

Bloom gelatin in water, set aside
Add mash sweet potato, sugar, milk and coconut milk in a heat proof  bowl.
Bain marie the mixture while using a whisk to stir and mix till combine. Remove bowl from heat.

I notice that my mixture is not smooth, so I use a immersion blender to blend the sweet potato mixture till smooth. You may choose to skip this step. Meanwhile, microwave your bloomed gelatin for about 10 seconds or till melted, pour into sweet potato mixture and combine. Set aside.

Using hand held blender, whip heavy cream till almost stiff peak.
Combine heavy cream into sweet potato mixture till mixed. Get ready to build your cake.

Sweet Potato Creme Patisserie
**This can be made one day in advance as you need to cool the creme.

450ml milk
1/2 vanilla bean or 1 tbsp vanilla bean paste
42g cornstarch
1/4 tsp salt
4 yolks
80g sugar
150g mashed sweet potato

28g butter

Prepare a flat pan with cling wrap. This is to cool the creme patisserie.
Pour milk, vanilla bean paste into pot.
Heat up milk over low to medium while stirring occasionally. Off heat when the milk mixture is about to boil.
Meanwhile, whisk egg yolk, sugar and salt together till light. Mix in cornstarch and mix together till combine.
Add the mashed sweet potato and mix together, you may find bits of sweet potato in this point. 
Pour 1/4 of hot milk mixture to yolk mixture, whisk slightly to combine. Slowly pour in remaining milk mixture to yolk mixture and whisk till combine. Your mixture will be warm.

If you are someone who wants a smooth mixture, a blender will be useful at this point of time. Just blend the milk mixture till the sweet potato bits are gone. If you are fine with it, then skip this step.

Pour the milk mixture back to the same pot.
Turn on fire in low to medium heat and using a spatula, stir your milk mixture. This is very important step I only use spatula because I notice using whisk, the air incorporate very quickly I will get over cooked custard. I prefer to use spatula.
Keep stirring the mixture and after about 1 minute, you will notice the mixture start to thicken. Keep on stirring in big circles and when you notice the whole mixture thicken, quickly remove pot and turn off fire. Keep stirring because the mixture will continue to cook. Add in the butter at this timing and mix together. Once the butter have melted, pour the cook creme over the flat pan.
Let it cool down and cover with cling wrap to prevent drying out. Keep the creme patisserie in a airtight container and keep in fridge. Mixture can be kept for 3 days.


Plain Sponge
Cut sweet potato cubes

Sweet Potato Mousse

Sweet Potato Creme Patisserie
100g heavy cream
20g icing sugar

Using a 6 inch square cake ring. Cut the sponge into two same pieces for the bottom and top.
Wrap your bottom cake ring with aluminium foil tightly. make sure there are no holes otherwise your mousse will leak.
Place first piece of sponge at cake ring bottom, add the cut sweet potato cubes.
Pour the sweet potato mousse over the cake base. Slightly wriggle to make sure the mixture cover all areas. 
Place the other piece of sponge over the mousse and slightly press the top.
Cover cake with cling wrap and refrigerate for at least 2 hours or till set. I prefer to chill at least half a day. 

Take about 70 grams of sweet potato creme patisserie and slightly re-beat the cold custard till smooth.
Combine heavy cream and icing sugar. Using a handheld blender, whip cream till almost stiff peaks.
Fold this into smooth sweet potato creme patisserie
Remove your cake from fridge and unmold the cake. Decorate cake top with sweet potato creme.

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